1. Field of the Invention
The invention relates to a pneumatic spring percussion mechanism in accordance with the preamble of claim 1.
2. Description of the Related Art
Pneumatic spring percussion mechanisms have been known for a long time, in particular for use in hammer drills and/or impact hammers. A common feature in the different types of pneumatic spring percussion mechanisms is that a driving piston moves axially in a reciprocating manner e.g. via a motor-driven crank drive. A percussion piston is co-axially disposed upstream of the driving piston in such a manner that a hollow chamber is formed, at least temporarily, between the driving piston and the percussion piston, which hollow chamber is sealed from the surroundings with the aid of the percussion mechanism housing. The air reservoir contained within the hollow chamber serves as a pneumatic spring when the driving piston moves and transfers the movement of the driving piston to the percussion piston so that this also follows the movement of the driving piston in a time-delayed manner and impacts against a tool shank or an intermediately connected riveting set.
Pneumatic spring percussion mechanisms are conventionally split into three groups. So-called pipe percussion mechanisms are thus known, wherein the driving piston and the percussion piston having the same diameter can move in the percussion mechanism pipe, as described for example in DE 198 43 644 A1. There are also so-called hollow piston percussion mechanisms, wherein the driving piston comprises a hollow recess on its end side in which the percussion piston can move (see DE 198 28 426 A1). The third group relates to hollow beater percussion mechanisms, wherein the percussion piston comprises a hollow recess on its end side facing the driving piston, in which recess the driving piston can move.
DE 198 28 426 A1 shows an example for an ordinary drive of the driving piston, wherein an electro-motor rotationally drives a crank shaft whose movement is transferred to the driving piston via a connecting rod and is transformed into an axial reciprocating movement.
It was always desirable to simplify the drive of the driving piston which is relatively costly in terms of mechanics. For this purpose, it was proposed e.g. in DE-PS 848 780 to drive the percussion piston with the aid of electromagnetic coils and to accelerate it against a tool shank. However, such a percussion mechanism is, in practice, subject to considerable thermal loads since the percussion piston is not only heated by the impact energy which is released during impact but also has eddy currents flowing through it, which in many cases even causes permanent damage to the percussion piston.